Steel Plate Heat Treatment for Shape Correction During Tempering
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Solution Overview
Problem
The existing method for producing steel plate members with hard and soft regions suffers from dimensional accuracy degradation due to thermal deformation during tempering, making it difficult to achieve precise dimensions.
Innovation Solution
A method involving quenching followed by a tempering process where the steel plate is heated above the austenite transformation finish temperature and then cooled rapidly, while a specific region is reheated above the austenite transformation start temperature but cooled at a slower rate than the lower critical cooling rate, allowing for shape correction within a defined temperature range to form a hard martensite region and a soft ferrite/pearlite region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the steel plate member is reheated during tempering to form a soft region, then the material properties are improved with a hard region containing martensite and a soft region containing ferrite and pearlite, but the accuracy of dimensions is degraded due to thermal deformation
Solution Approach 1:
The steel plate member is divided into a hard region and a soft region through selective heating. The hard region is heated to form martensite while the soft region is heated to a lower temperature to form ferrite and pearlite, achieving spatial segmentation of material properties to simultaneously obtain strength and ductility
Solution Approach 2:
The invention controls the heating temperature parameters during tempering to achieve different microstructures. By precisely controlling the heating temperature in different regions (above Ac3 for hard region, between Ac1 and Ac3 for soft region), the transformation products are controlled to achieve the desired combination of hardness and softness while minimizing thermal deformation
2Manufacturing precision
If the steel plate member is corrected after tempering to improve dimensional accuracy, then the shape is adjusted, but it is difficult to sufficiently improve the accuracy of the dimensions
Solution Approach 1:
The invention performs shape correction during the tempering process itself, before the final cooling and solidification. By applying correction forces while the material is in the austenite or transformation state (when it has different mechanical properties and is more formable), the dimensional accuracy is improved without requiring additional post-processing steps
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the accuracy of dimensions in steel plate members by enabling easy shape correction with minimal power and improves energy efficiency and strength in the soft region.
Implementation Method 1
heating the steel plate member to a temperature higher than an austenite transformation finish temperature A3 and subsequently cooling the steel plate member at a cooling rate faster than an upper critical cooling rate
Implementation Method 2
reheating a second region of the steel plate member to a temperature higher than an austenite transformation start temperature A1 without reheating a first region of the steel plate member after quenching and subsequently cooling the steel plate member at a cooling rate slower than a lower critical cooling rate
Implementation Method 3
the shape of the second region is corrected in a temperature range from a temperature that is equal to or lower than the austenite transformation start temperature A1 to a temperature that is equal to or higher than a temperature at which transformation into ferrite and pearlite is finished while maintaining the cooling rate slower than the lower critical cooling rate
Data Source
AI summary
A method for producing a steel plate member (SPM), including: a quenching step for heating the SPM to a temperature higher than an austenite transformation finish temperature A3 and subsequently cooling the SPM at a cooling rate (CR) faster than an upper critical CR; and a tempering step for reheating a second region of the SPM to a temperature higher than an austenite transformation start temperature A1 without reheating a first region of the SPM after quenching and subsequently cooling the SPM at a CR slower than a lower critical CR. In the cooling process of the tempering step, the shape of the second region is corrected in a temperature range from a temperature equal to or lower than A1 to a temperature equal to or higher than a temperature at which transformation into ferrite and pearlite is finished while maintaining the CR slower than the lower critical CR.